Collecting and recording the operating data of a motor vehicle is becoming more and more important (see also German Patent No. 199 14 764). The operating data are supplied by appropriate sensors and are generally made available in digital form. The operating data can be, for example, the speed of the motor vehicle, the temperature and the operating point of an internal combustion engine of the motor vehicle, the activation of the gas pedal or brakes, or the activation of specific motor-vehicle functions, in particular, the illumination or the directional lights. The operating data are recorded over time. Because the storage space is limited in a control device for controlling/regulating specific motor-vehicle components or in an operating- or accident-data recorder in a motor vehicle, it is necessary to reduce the data volume to be stored.
The data volume can be reduced in different ways. First, redundancies in the information to be stored can be avoided, i.e., identical bits of information are stored only once.
Furthermore, the data volume to be stored can be reduced through a data reduction. In this context, when being stored, information that is not viewed as relevant is dispensed with in a controlled manner. In the data reduction process, the non-relevant information content is omitted in a controlled manner. The original information can be reconstructed from the reduced information but only at a loss of information.
Finally, the information to be stored can be reduced by data compression. In this context, the number of bits necessary for storing and transmitting the information is reduced. The original information can be reconstructed without any loss of information by decompressing the compressed information.
While for data compression, very many different methods are known, specifically in the area of image data compression and information technology (e.g., Huffmann Compression; see H. Y. P Lim, “Interactive Data Compression Tutor,” School of Electrical and Electronics Engineering, Birmingham, UK, February, 1998), as well as methods for the reconstruction of time signals, that are based on the Shannon scanning theorem (e.g., impulse train modulation; see A. V. Oppenheim, R. W. Schaefer, “Discrete-Time Signal Processing,” Prentice-Hall, Englewood Cliffs, 1989), for data reduction there exists no generally applicable method, because a loss of information is always inevitable and therefore a function of the application.
From European Patent No. 0 834 146, a method and a device are known for the data-reduction of scanned information in an implanted medical device. The scanned information is, for example, the heart rate of a patient. It is proposed to store the time interval between two heart beats not as a time indication, but rather to assign to each time indication a specific value, which requires less storage space than the actual time indication, and then to store this value.
From German Published Patent Application No. 41 07 198, a method and a device are known for recording the operating data of a motor vehicle. To reduce the requirements for storage space, it is proposed to delete from the memory information that is older and no longer necessary. The storage space that is freed up can then be used to store current information.
A method and a device of the type cited above are known, for example, from German Published Patent Application No. 43 44 528. In that publication, a device is described for storing information in the form of digital audio signals. After a data reduction and a digital/analog (D/A) conversion, the information to be stored is saved as analog values in an analog storage. Although this publication refers to data reduction, it is really a matter, in this context, of data compression. As a method for data compression, Adaptive Differential Pulse Code Modulation (ADPCM) and Linear Predictive Coding (LPC) are proposed. The stored information can be retrieved from the memory as audio signals via an analog/digital (A/D) inverse conversion.